Aircraft landing gear



Sept. 1, 1936. R. A.swA| M AIRCRAFT LANDING GEAR Filed July 3o,v 1932 Q h n INVENTOR Ruger] SW/m ATTORNEY .Patented Sept. 1, 1936 AIRCRAFT LANDING GEAR Robert A. Swalm, Buffalo, N. Y., assignor to Curtiss Aeroplane & Motor Company, Inc., a corporation of New York Application July 30, 1932., Serial No. 626,393 4 Claims. (Cl. 267-64) This invention relates to aircraft landing gears, and more particularly to improvements in airhydraulic shock absorbing struts for embodiment in aircraft landing gears.

The usual aircraft landing gear comprises one or several struts pivoted to the body of the aircraft, certain of the struts depending from the aircraft and having attached at their lower extremities a stub axle and a Wheel for ground contact. At the upper ends of the struts provision is made for a shock absorbing mechanism to absorb the impact of landing and to provide `a resilient support, acting as a spring when the airplane travels over rough, uneven ground, thereby absorbing ground shocks and preventing their transmission from the ground to the body of the aircraft. My invention isl particularly concerned with an improved form of an oleo or hydraulic shock absorbing strut. Some shock absorbing struts in the past have combined the advantages to be derived from hydraulic action for shock absorption, and the resilient action of compressed air for aiding in shock absorption and for giving a resilient action to the strut. It has previously been found necessary to use air under considerable pressure in such struts, resulting in mechanical diiculties in the sealing of this compressed air within the shock absorber. It is Well known that air or iiuid under pressure will gradually leak through the smallest openings, and with the packing glands usually incorporated in such shock absorbers, retention of air pressure or the `full quantity of iluid over a long period of time has been diicult. Service conditions in operation make it inconvenient to determine whether such air pressure is adequate, or whether there is suiicient iluid in the strut to insure safety.

An object of my invention is to. provide a hydro-pneumatic shock absorbing strut in which the air pressure is substantially atmospheric when the shock absorbing strut is extended. By this arrangement, sealing of the shock absorbing strut against loss of air pressure becomes a minor problem rather than a major problem.

An additional object of my invention is to provide a novel form of packing gland with pressure relief passages so that the packing is at no time subjected to excessive pressures, thereby lengthening its life and increasing its eiiiciency in eliminating loss of hydraulic uid from the shock absorbing strut.

A further object of my invention is to provide a reservoir for hydraulic fluid which automatically allows additional fiuid to pass into the shock absorbing strut to make up for any slight loss that might occur through the packing gland.

A further object of my invention is to provide a novel form of valve to regulate the speed of action of the shock absorbing strut under load. 5 In addition, this valve provides for high resistance to motion of the shock absorber at extreme positions of adjustment, preventing damage to the shock absorbing strut when severe pressures are imposed upon it while the shock absorbing 10 strut is in an extreme position of adjustment.

A further object of the invention is to provide a novel form of relief valve in the hydraulic mechanism, whereby high impact stresses serve to automatically retard the rapid compression of the shock absorbing strut, and whereby restitution of the shock absorbing strut to an extended position may be effected without a restriction of the ow of the hydraulic iiuid.

An additional object is to provide an air cushion for supporting .the weight of the aircraft when it is traveling over the ground, and to so arrange the mechanism that impact stresses are largely assumed by hydraulic action, while taxiing stresses are largely assumed by the 'air cushion.'

In the drawing, wherein similar reference characters designate similar parts,

Fig. 1 is a view partly in section and'partly in elevation, showing the details of construction of the shock absorbing strut; and

Fig. 2 is a view similar to Fig. 1 showing the shock absorbing strut in a partially compressed condition.

The shock absorbing strut I0 comprises a plunger II having a closure I2 at its upper end. To the closure is attached an eye I3 for attachment of the shock absorbing strut to the aircraft. The plunger II is adapted to slide within a cylinder I4, having at its bottom end a closure I5 provided with an eye I6 for attachment to the landing gear of the aircraft. Suitable means external of the shock absorbing strut ID or in conjunction therewith may be supplied to limit the extension of the eyes I3 and I6 so that the plunger II is at all times retained within the cylinder I4.

The closure I5 of the cylinder I4 carries a metering pin I'I extending into the cylinder along its axis. The metering pin I 'I is tapered to a` small diameter at its mid portion I8, or is other- Wise constructed so that the cross sectional area of the mid portion I8 is substantially less than the end portions I9 and 20. A bulkhead 2| is rigid with the lower end of the plunger II, and has formed therein an orifice 22 of slightly greater diameter than the end portions I9 and 20 of the metering pin II. In the extended position of adjustment of the shock absorbing strut I0, the end portion 20 of the metering pin I1 lies within the orice 22. Upon compression of the shock absorbing strut, the plunger III telescopes within the cylinder I4 and the bulkhead 2| slides down over the metering pin I'I, as shown in Fig. 2, whereupon the eiectivearea of the orifice 22 is increased as it embraces the smaller mid portion I8 of the metering pin I' The eiective area of the orifice 22 is thus gradually decreased as it approaches the enlarged portion I9 of the metering pin Il. The cylinder I4, and part of the plunger I I, are filled with iluid in a manner to be later described.

'Ihe bulkhead 2| has formed therein an annular recess 23, just below the orice 22. A disc flap valve 24, having an opening 25 of slightly Y larger diameter than the portion 2l) of the metering pin |'I and of slightly smaller diameter lthan the orifice 22, surrounds the metering pin. The valve 24 is retained against the bulkhead 2| by means of screws 26 engaging in holes 21 in the valve. The screws 2G allow the valve 24 to move against the bulkhead ZI or away from it according to the direction of flow of the fluid through the orifice 22. As compressive stresses are applied to the eyes I3 and I6, the plunger |I starts to move into the cylinder I4, therebyexerting pressure on the fluid within the cylinder.. I4 and tending to force it through the orifice 22. This ow ofl uid likewise causes a pressure to be exerted on the lower surface of the valve 24,

causing it (the valve) to move against the bulkhead 2|, further restricting the effective area through which the fluid may pass. Accordingly, the only passage for the fluid is that provided by the opening 25 and the oriice 22, restricted by the metering pin Il. By this action, great resist-` ance is built.up to the movementof iluidfrom the cylinder I4, and the telescoping ofthe plunger Il with respect to the cylinder I5 is thereby retarded. As the motion progresses, the smaller tapered portion of the metering pin is made to coincide with the opening 25 and the orifice 22 and the flow of fluid through the then enlarged opening is thereby allowed to increase, whereupon telescopingl motion of the plunger within the cylinder Ill accelerates. After` the portion I8 of the metering pin II passes beyond the openings 22 and 25, resistance of flow again cumulatively increases as the openings approach the portion I9 of the metering pin I'I, at which timey the maximum imposed shocks upon the mechanism will have been eiectively damped. As the fluid within the cylinder Ill is fmoved vthrough the orice 22 andthe opening 25,"the'air trapped within the plunger II is compressed, and upon cessation of the externally applied compressive stresses, the resilient action of the compressed air will tend to eject the uid from the plunger II and effect restitution of the shock absorbing strut I0 to its extended position. Upon initiation of such restitutional force, the pressure of fluid on the upper side of the bulkhead 2|, passing through the orice 22, causes the ap valve 2li to snap back against the heads of the screws 25 allowing for freer flow of the uid through the orice 22 alone. The restitutional effect continues until the shock absorbing strut Il) is again returned to its extended position as in Fig. 1.

Briefly summarizing the action of the shock absorbing strut I0, the metering pin II may be said to prevent excessively fast movement of the fluid and hence of the plunger with respect to the cylinder I4 at extreme positionsof travel in either direction. The ilap valve 24 furnishes an additional restriction to the passage of fluid with a resultant retarding eiect upon the speed of compression of the shock absorbing strut, this additional restriction being relieved upon extension of the strut. When the airplane rests or rolls on the ground, kthe shock absorbing strut ||l assumes a position as in Fig. 2, the air compressed within the plunger balancing thev weight or compressive force imposed on the strut.

The construction and action of the packing gland 28 and its associated parts carried by the cylinder I4 and engaging the plunger I Ir will now be described. In the upper portion of the cylinder I4 is an annular groove 29 having an upper threaded portion 30. Suitable packing material 3| is placed within the annular groove 29 around the plunger I I, this packing being being retained in proper position by a packing nut 32 screwed into the threads 30. Just below the annular groove' 29, a series of openings or ports 33 is formed in thewall of the cylinder I4, which openingsv may be connected by an annular groove 34. The groove 34 is at all times covered by the plunger I I. .At some distance below the openings 33 is an additional port or opening 35 also formed in the wall of thevcylinder I4. The port 35 is located at such a position that it allows communication between the inside-of the cylinder I4 and the outside of said 'cylnder whenthe plunger |,is in its extended position. Immediately upon movement of the plunger II within the cylinder I4, the plunger covers the port 35. Around the outside `of the cylinder I4 anannular reservoir 36 is formed,said,reservoir Vhaving a height sufficient to embrace the o'p`ening's`33l and 35. The

reservoir 36' is fittedgwith `a liller opening 31 intowhich a plug 38may be screwed. At the upper'end of thereservoir 36. agthreaded vent` opening`39 is formed lint aplug 40 'may be screwed. Revertingtothe'plung'er I |,a threaded vent opening 4| is'formed at the upper portion thereof, into which isv screwed a plug '42.

In lling the shock absorbing strut with uid, the plugs 38, d and 42 are removed and hydraulic iluid is poured into the opening 31 until the fluid level Vreaches said opening. In filling, the uid passes through the port 35, completely filling the lower portion of the cylinder I4, and as the level is increased, a certain amount of the fluid passes through the oriilce 22 so that the final level of fluid within the reservoir 36, the cylinder i4 and the plunger II, is equal. The vent openings 39 and 4| admit of the escape of airas the fluid enters and displaces air from the Vcompartments in which these openings are formed. Upon .lling of the shock absorbing strut 'Ill to the proper level, the plugs 38, 40, and 42are tightly screwed in, whereupon the air within the reservoir 36 and within the plunger II is sealed, under atmospheric pressure. The Vshock absorbing strut is then in condition ,for operation.

Astelescoping action of the plunger II within the cylinder III takes place, as previously described, the port 35 is closed by the plunger II and the pressure of air and iluid within the shock absorbing strut tends to cause creepage of fluid in the small clearance space between the inner wall of the cylinder I4 and the outer Wall of the plunger II. This creepage progresses as far as the opening 33, whereupon` the iluid passes through the opening 33 and into the reservoir 36, the pressure in the reservoir 36 having been maintained at atmospheric upon closing of the port 35 by the plunger II. Hence, the uid pressure within the shock absorbing strut I D cannot be transmitted above the opening 33, and, since the packing gland 28 is above the level of the opening 33, the packing gland 28 is isolated from high pressure, and hence, from leakage.

Upon restitution of the shock absorbing strut to its extended position, the opening 35 is again uncovered by the plunger I I and an atmospheric pressure balance is automatically effected between the air and-fluid in the reservoir 36, and the air and fluid within the cylinder Id' and the plunger I I. Over a period of time, while the shock absorbing strut I is in an extended position during ilight, a slight seepage of air may take place between the packing gland 28 and the plunger ll, which is transmitted into the reservoir 36 through the opening 33, thereby automatically establishing a balanced atmospheric pressure condition within the shock absorbing strut, which pressure balance may have become slightly upset during rapid action of the shock absorbing strut while the aircraft was taxiing and taking oi.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to those skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. I' aim in the appended claims to cover all such modifications and changes.

What is claimed is: K

1.In a hydraulic shock absorber capable of deection and extension, a cylinder, a hollow plunger slidable in said cylinder, a reservoir carried by said cylinder and open to the interior thereof toward one end thereof and also open thereto intermediate the length thereof, said plunger being adapted at all times to close said end opening, and being adapted to open said intermediate opening only when said shock absorber strut is extended.

2. In a substantially vertical hydro-pneumatic shock absorber, a cylinder, a hollow plunger adapted to slide within said cylinder and having an opening in its lower end through which iluid is adapted to pass,a reservoir encircling the upper end of said cylinder said cylinder having an upper internal annular groove and openings leading to said reservoir and having lower openings leading to said reservoir, said plunger being adapted in its extended position to cover said groove and to uncover said lower openings, and in its telescoped position, to cover said groove and said lower openings; a packing gland at the upper end of said cylinder above said groove engaging said plunger, and means carried by said reservoir for allowing said reservoir and said cylinder to be iilled to a predetermined level.

3. In a hydro-pneumatic shock absorber including a hollow plunger slidable in a cylinder, packing means carried by said cylinder for engagement with said plunger, said cylinder having an opening in its wall below said packing adapted to be covered by said plunger in all positions of contraction or expansion of the shock absorber, and a reservoir adjacent said cylinder with which said opening communicates at all times, said opening serving to allow iiuid iiow from between said cylinder and plunger to said reservoir whereby pressures generated between said cylinder and said plunger are prevented from reaching said packing.

4. In a hydro-pneumatic shock absorber strut having a hollow plunger slidable within a cylinder, said plunger having a head and a metering orifice therein through which fluid is adapted to flow from said cylinder upon compression of said strut, means for maintaining the fluid level within said strut comprising a iiuid reservoir carried by said cylinder, said cylinder having a wall opening just below the plunger head when the latter is extended, said opening allowing, when said strut is extended, free fluid flow between said cylinder and said reservoir, and a packing gland on said cylinder engaging said plunger, said cylinder ,having a second opening communicating with said reservoir at a point along the wall of said cylinder which is covered by said plunger in all positions of adjustment thereof, said second opening forming a relief to by-pass fluid under high pressure to said reservoir.

ROBERT A. SWALM. 

